Disadvantages of really lean AFR for cruising

[Peace]

Hello everyone.
I'm using ECR33 with Rb25DET onboard. It is controlled by Z32 ECU with nistune type 2.

Can some one tell me what is the disadvantages of having lean (16-17) AFR at the cruise ander low load (firs two columns of TP)?

I've set my car now for this and as far i cant see any disadvantages, car cruise smooth until AFR goes to 18. As far as i push the gas AFR goes to 12 and everything fine.

I only interested what bad can be in such len AFR on cruising

[Legionnaire]

high content of nitrogen oxides in your exhaust, i guess. Otherwise, if egts are in check and no negative mechanical effects encountered, it's ok.

BTW, have you noticed any significant reduction in fuel consumption with the tune like this? if so then by how much?

[mattminer]

We do this commonly on hondas, jsut watch for EGTs and driveability. WE usually get lean cruise up around 17:1 withough issue on b and d series hondas. On the other hand, EJ Subarus wont take anything leaner then about 15:1 withotu stumbling.

i was able to pick up almost 10mpg on my honda, on average street driving with lean cruise.

[Peace]

Fuel consumption was not yet counted, because i've not finished with my car. Waitin for new engine and just experimenting now.

Drivability is good on AFR up to 18.

[raddy]

I just tested my ca18det with AFR 17:1 at cruising, without any problems. At 18:1 it start runing rough.

[gunni]

The only indicator of actual lower usage is the change pulsewidth at cruise.
or a dyno.

If you start dropping power then you need to open the throttle for more air , and more air needs more fuel.

[IceManPL]

so you can try to advance ignition a little bit to compensate this decrease of power
it should work

[gunni]

You should already be at MBT anyway is my saying.

Lean doesn´t automatically mean better mileage.

[Legionnaire]

Let's put it this way: it depends on what you are trying to do - accelerate, move at fixed speed or something else. If it is cruising then leaner may actually mean more MPG (KPL )

[Peace]

Yes.
I'm telling exacly about cruising - maintaining speed.
It looks like it saved me about 4 litres per 100 km.

Now i got new engine in an messed map completley. Got lean idle and cruising and realy rich transition area =)

Anyway it looks like fuel consumption is 18l per 100km wich is nice since i'm realylove to drive WOT =)

[Legionnaire]

18l per 100km is a lot for cruising - what speed do you usually "cruise" at to spend this amount of fuel?

[Peace]

This is not for cruising this is for city cycle. I'm cruising about 15-20% of my driving in a city.
I have lean only at cruising thought.

[RomChip200]

18L / 100km is still to much for city driving if you run unleaded fuel.
It's what I got on my 300 but with E85 ....

I run 16.5-17 AFR when cruising, the problem is not 17 value but the transitions on the throttle when you need a bit more (even when cruising) and I think it affects more the fuel mileage b/c the engine struggles more from 17 to 14 than 15 to 14.

[pexzed]

I run about 16:5 to 1 on my '90 300zx as reported by the pair of WBO2s I use (PLX + Bosch sensors x 2).
Once I lean out to about 17:5 to one, the engine starts to miss-fire.
I also have the ECUtalk display, and it reports about 9.5 litres per 100km while using the cruise control on a flat road at 100km/h.
The last dyno was 330 rwkw, so I have good aspects of economy and power.

[RomChip200]

As for me, I may run leaner on E85.
I got 13L/ 100kms on highway and I got 10.5L /100kms before with unleaded.